Presynaptic mechanisms controlling excitatory and inhibitory synaptic transmission in the cerebral cortex have critical roles in normal information processing and also may contribute to the pathophysiology of a variety of brain disorders such as cognitive decline and epilepsy. The specific aims of these experiments focus primarily on inhibitory synaptic transmission mediated by gamma-amino butyric acid (GABA)-containing inhibitory interneurons and its regulation by 3 potent and ubiquitous processes in normal cerebral cortex and in a model of posttraumatic epileptogenesis. These neurons are known to be vulnerable to injury. Specific aims relate to (1) control of transmitter release by presynaptic Ca++ channels and (2,3) modulatory effects on GABAergic inhibition produced by actions of neuropeptide Y and GABA at their receptors and selective Ca++ current blockers on presynaptic terminals of major classes of inhibitory interneurons. Techniques employed include use of whole cell patch clamp recordings of spontaneous and evoked inhibitory postsynaptic currents (IPSCs) generated by identified subclasses of interneurons in in vitro brain slices;laser scanning photostimulation to map cortical connectivity;paired recordings to examine unitary IPSCs from interneurons to other interneurons and pyramidal cells;use of genetically engineered mice with GFP label in specific interneuron species;and local application or bath perfusion of receptor agonists and antagonists. The partial cortical isolation model will be used to provide chronically injured, epileptogenic neocortical slices and assess changes in these presynaptic modulatory mechanisms that might contribute to hyperexcitability. The long term goals are to identify critical abnormalities that might eventually be targets for selective agents that would used to prevent or treat human posttraumatic epilepsy. PUBLIC HEALTH RELEVANCE: Epilepsy following brain injury is a major health problem. The mechanisms that lead from injury to epilepsy in man are poorly understood however loss of the ability to inhibit or "quiet" nerve cells with the chemical messenger, GABA, is one key underlying factor. The proposed experiments will use a model of posttraumatic epilepsy to better understand how nerve cells regulate GABA release in normal and injured brain, what might go wrong after brain injury, and how that knowledge might be used to improve approaches for prevention and treatment of epilepsy.